With advances of the trend for high-definition of image quality in ink jet and with expansion of a range of application in industrial uses in recent years, demands for minute pattern formation and for ejection of high viscosity ink have been strengthened increasingly, and there have been advanced the development of the liquid ejection device for solving the aforesaid subjects and of the method for its manufacturing (for example, see Patent Documents 1-5 listed below).
Among them, as a technology to eject not only low viscosity droplets but also high viscosity droplets from a miniaturized nozzle to meet the aforesaid demands, there is known a droplet ejection technology of the so-called electrostatic suction method wherein a liquid in a nozzle is charged, and liquid ejection is carried out by electrostatic attraction force that is received from an electric field that is formed between a nozzle and various types of base member serving as objects to receive impact of droplets.
Further, there is advancing development of a droplet ejection device employing the so-called electric field assist system which is a combination of this droplet ejection technology and a technology to eject droplets by utilizing pressure caused by deformation of piezoelectric element and by generation of bubbles in a liquid.
This electric field assist system is a method wherein a meniscus of a liquid is protruded at a liquid ejection opening of the nozzle by the use of a meniscus forming device and an electrostatic attraction force, to enhance the electrostatic attraction force for the meniscus and to overcome the liquid surface tension so that the meniscus may be made to be droplets to be ejected.
In the electric field assist system, a droplet is formed from a nozzle by the resultant force of the pressure and the electrostatic attraction force as stated above, and the droplet thus formed is caused by electrostatic attraction force to fly to base member, therefore, the impact ability for a minute droplet is more improved than those of the conventional piezoelectric method and a thermal method.
Further, in the conventional piezoelectric method or the thermal method, the total energies for forming a meniscus and for causing it to fly to impact against a base member need to be covered by pressure caused by deformation of the piezoelectric element and the like, while, energies needed for generating pressure required in the electric field assist system are only energies for forming a meniscus and for forming a droplet. Therefore, a drive voltage for a pressure generating device composed of a piezoelectric actuator such as a piezoelectric element can be lower than that for the conventional method, which is an advantage.    Patent Document 1: Unexamined Japanese Patent Application Publication No. 2005-249436    Patent Document 2: Unexamined Japanese Patent Application Publication No. H08-85212    Patent Document 3: Unexamined Japanese Patent Application Publication No. 2004-503377    Patent Document 4: Unexamined Japanese Patent Application Publication No. 2000-229423    Patent Document 5: Unexamined Japanese Patent Application Publication No. 2002-355977